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Inspec coverage of the experiments at the LHC, CERN

By Chris Marker 2011

Why are we here?

Science, and in particular physics from the time of Socrates onwards, has always tried to answer the big questions such as “What is the Universe around us made of?” and “What are the laws that govern the workings of this Universe?” The Large Hadron Collider (LHC) at CERN aims to answer these questions by colliding proton beams or lead ions together.

The Inspec classification scheme can be used to tell the story of the experiments that are taking place at the LHC. The main task of the LHC is to explore the standard model of particle physics which describes three of the four known fundamental interactions (gravity being the odd one out) among the elementary particles that make up all matter. The LHC does this by colliding beams of protons together at an energy of 14 TeV producing a multitude of subatomic particles.

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Relativity and gravitation

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Standard model of unification

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Hadron induced very high energy interactions interactions (E > 1 TeV)

The interactions and decays of these particles can be detected and analysed to probe the standard model. There are four radiation detectors located at the LHC each of which looks at a specific area of research.

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Radiation detectors

It is hoped that one of the particles produced by the LHC will be the elusive Higgs boson, the so called “God particle”, that is thought to give all other particles mass. The ATLAS and CMS detectors will be the primary detectors in the search for the Higgs.

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Intermediate and Higgs bosons

The LHC could also give an insight into what the Universe is made of. All that we can see in the Universe, stars, planets etcetera make up only 4% of the Universe. The other 96% is made from dark matter and dark energy which are very difficult to detect but which we know must exist due to the gravitational forces that they exert.

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Cosmology

Candidates for the particles to make up dark matter are sparticles. These are supersymmetric partners of the normal particles that make up matter.

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Supersymmetric particles

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Supersymmetry in particle physics

Detecting sparticles could also point the way to a unification of all of the four forces of nature.

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Unified models beyond the standard model

Along with normal matter, antimatter was created in an equal amount in the Big Bang at the beginning of the Universe. These two forms of matter should, according to theory, have completely annihilated each other leaving literally nothing and meaning that we should not be in existence. The LHCb detector will look into possible differences between matter and antimatter especially a symmetry known as charge parity violation.

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Charge conjugation, parity, time reversal and other discrete symmetries

As well as colliding protons together, the LHC will also collide lead ions in an effort to create a quark-gluon plasma (quarks and gluons are elementary particles). This plasma is thought to have existed a few microseconds after the Big Bang. Studying the properties of the plasma at the ALICE detector will thus give clues as to the origin and early evolution of the Universe.

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Nuclear matter

In addition the LHC will look for signs of extra dimensions beyond the normal four. Detecting these dimensions could lead to advances in string theory and superstring theory which are candidates for a “theory of everything”.

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Theories of strings and other extended objects

In a way it will be more exciting if the LHC does not find the coveted Higgs! If something totally unexpected crops up this will lead to new theories and experiments. Whatever is found by the LHC is it is sure to be an exciting and vibrant time for all physicists.